Waveguides

ABSTRACT

A dielectric waveguide comprising a dielectric probe at each end, wherein the dielectric probes are arranged to transfer energy.

TECHNICAL FIELD

The present invention relates to waveguides, and particularly, althoughnot exclusively to low cost dielectric waveguides forsub-millimetres/Terahertz(sub-mm/THz) applications.

BACKGROUND

Waveguides is an indispensible technology widely used in differenttechnology fields such as wireless and wire-line communications,metrology, sensing and security. In particular, dielectric waveguideshave been used in transmission line applications as well as in waveguidecircuits to confine, process and transmit light over various distances.For example, dielectric waveguides are used to transmit light overthousands of kilometers (km) in long-distance fibre-optic transmission.In another application, dielectric waveguides are used in integratedphotonics for light processing and transmission over tens or hundreds ofmicrometers (μm).

Dielectric waveguides of different size, shape, material and form arerequired for different applications. For sub-millimetres/Terahertzfrequency applications of guided-waves, waveguide circuits with smalldimension are desired in order to satisfy the associated single-mode andmodal-operation conditions. However, the fabrication of small dimensionwaveguides, especially those made with metallic materials isparticularly challenging. Moreover, metallic waveguides forsub-millimetres/terahertz frequency applications are relativelyinflexible and costly to manufacture.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there isprovided a dielectric waveguide comprising a dielectric probe at eachend, wherein the dielectric probes are arranged to transfer energy.

In an embodiment of the first aspect, a core or a cladding or both thecore and the cladding of the dielectric waveguide are made of polymericmaterials.

In an embodiment of the first aspect, the polymeric materials includethermoplastics or a combination of thermoplastic materials.

In an embodiment of the first aspect, the polymeric materials includeone of polyethylene or polypropylene or combinations thereof. In anembodiment of the first aspect, the dielectric waveguide is fabricatedby injection moulding.

In an embodiment of the first aspect, the dielectric waveguide isfabricated in a single mould.

In an embodiment of the first aspect, the dielectric waveguide is aplanar waveguide.

In an embodiment of the first aspect, the dielectric probes are tapered.

In an embodiment of the first aspect, the dielectric probes have alinear tapered form. In an embodiment of the first aspect, thedielectric probes are power adaptor probes.

In an embodiment of the first aspect, the dielectric waveguide isarranged to operate at sub millimeter (Sub-mm) or terahertz(THz)frequencies. In an embodiment of the first aspect, the terahertz (THz)frequencies comprise frequencies larger than 60 GHz.

In an embodiment of the first aspect, the dielectric waveguide has apropagation loss less than 0.5 dB/cm.

In an embodiment of the first aspect, the dielectric waveguide isfabricated in multiple moulds.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 shows a plurality of dielectric waveguides in accordance with oneembodiment of the present invention having different dimensions;

FIG. 2 is a graph showing the measured refractive indices and absorptioncoefficients in different frequencies for thermoplastic materials(polyethylene and polypropylene) that can be used to fabricate thedielectric waveguides of FIG. 1;

FIG. 3 shows a vector network analyser (PNA-X) instrumentation with WR-5and WR-22 metallic tapers for measuring and characterizing operationcharacteristics of the dielectric waveguides of FIG. 1; and

FIG. 4 is a graph showing the operation characteristics (coupling lossand propagation loss) of the dielectric waveguides of FIG. 1 indifferent frequencies measured using the setup of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is illustrated an embodiment of a dielectricwaveguide comprising a dielectric probe at each end, wherein thedielectric probes are arranged to transfer energy.

In this embodiment, the waveguide 100 is a dielectric waveguide arrangedto be used for sub-millimetres/terahertz(sub-mm/THz) frequencyapplications of guided-waves. Preferably, the operation frequency of thewaveguide 100 is above 100 GHz. More preferably, the operation frequencyof the waveguide 100 is above 60 GHz. In other embodiments, thedielectric waveguide 100 can be arranged to be used in otherfrequencies.

As shown in FIG. 1, each dielectric waveguide 100 have a substantiallyrectangular portion 102 and two linearly tapered ends 104. In otherembodiments, the tapered ends 104 need not be linear and portion 102 ofthe waveguide 100 need not be rectangular. Portion 102 and the taperedends 104 can be of any other shape and form. In yet some otherembodiments, the dielectric waveguides 100 may not have any tapered ends104. As shown in FIG. 1, the length of the rectangular portion 102 ofthe waveguides 100 ranges from about 10 mm to about 40 mm whereas thelength of each tapered end 104 is about 32 mm. However, depending onapplications, the lengths of the rectangular portion 102 and the taperedends 104 can be lengthened or shortened. Preferably, the dielectricwaveguide 100 is a planar waveguide having a core sandwiched betweencladding layers (not shown). In other embodiments, the dielectricwaveguide 100 may be non-planar and can have other forms.

The dielectric waveguide 100 as shown in FIG. 1 is made of polymericmaterials. In particular, in some embodiments, only the core or thecladding of the dielectric waveguide 100 is made of polymeric materials.In some other embodiments, both the core and the cladding of thedielectric waveguide 100 are made of polymeric materials. Preferably,the polymeric materials used to fabricate the dielectric waveguide 100include thermoplastics or a combination of different thermoplasticmaterials. In a preferred embodiment, the thermoplastic materials usedare polyethylene, polypropylene or combinations thereof. In theembodiment as shown in FIG. 1, the dielectric waveguides 100 areair-clad polyethylene-core waveguides fabricated by injection mouldingin a single mould. Alternatively, multiple moulds may be used in someother embodiments where the waveguide 100 comprises multiple materialsor has a complex structure.

To measure the optical properties of polyethylene and polypropylene,materials that can potentially be used to make the dielectric waveguides100 of FIG. 1, a pulsed THz time-domain spectroscopy (THz-TDS)instrument is used (not shown). Plastic samples in the form of slabs ofvarious thicknesses are measured and their time-domain transmittedsignals are compared with reference signals (not illustrated).

The refractive indices and absorption coefficients of polyethylene andpolypropylene materials measured in different frequencies are shown inFIG. 2. With reference to the absorption coefficient curves in FIG. 2,both polyethylene and polypropylene exhibit excellent transmissionability, with absorption coefficient well below 1 cm⁻¹ under 1 THz. Onthe other hand, polyethylene has a slightly higher refractive index thanpolypropylene over the entire frequency band. This shows thatpolyethylene and polypropylene are particularly suitable to be used ascore and cladding materials in dielectric waveguides. Therefore, withthese intrinsic propagation properties, flexible planar dielectriccircuits can be made with a combination of different thermoplasticsmaterials such as polyethylene and polypropylene.

Referring now to FIG. 3, there is shown a robust vector network analyzer(PNA-X) instrumentation 300 arranged to measure and characterize theoperation characteristics of the rectangular waveguides 100 of FIG. 1.The PNA-X analyser 300, with its metallic rectangular waveguideinterfaces 302 as I/O ports, presents a challenge in efficientconnecting with the dielectric waveguides 100 under test. To mitigatethis problem, the I/O waveguides 302 operating at 140 GHz to 220 GHz isexpanded from the standard WR-05 (1.3 mm×0.65 mm) to a larger WR-22 (5.6mm×2.8 mm) via a commercial mode convertor in the setup.

Since the mode profiles between the metallic waveguides 302 of theanalyser 300 and the dielectric rectangular waveguides 100 aredifferent, dielectric probes 104 that are linearly tapered in both x andy directions are arrange at both ends of the dielectric waveguide 100for transferring energy smoothly to and from the I/O ports 302 over abroad range of frequency. The incorporation of these probes 104 to thedielectric waveguides 100 can be easily accomplished by using injectionmoulding in which complicated structures can be made in a single ormultiple moulds.

FIG. 4 shows the operation characteristics of the rectangularpolyethylene waveguides 100 of FIG. 1 in different frequencies measuredusing the setup of FIG. 3. In particular, FIG. 4 shows the extractedcoupling loss of the tapered dielectric probes 104 and the propagationloss of the dielectric waveguides 100 over the band of 140 GHz to 220GHz. These losses are determined from the y-intercept and the slope ofthe curve relating the transmitted power versus dielectric waveguidelength (not shown).

As the coupling loss is due to two transitions, the coupling loss pertransition between the metallic and the dielectric waveguides should behalved. As shown in FIG. 4, the coupling loss measured increasesproportionally with frequency. This increase in coupling loss is likelydue to unwanted excitation of higher order modes into the over-modeddielectric waveguides 100. At frequencies below 170 GHz, the couplingloss can be as low as 1 dB per transition. Since only linearly taperedprobes 104 are used in this measurement, one can expect that thecoupling loss can be further reduced with an optimized probe designhaving a different shape and form. The propagation loss for thedielectric waveguide 100 of FIG. 1 is below 0.5 dB/cm over the entirefrequency band. This result is comparable to or better than resultsreported for other waveguide platforms.

The embodiments of the present invention are distinctive in that thethermoplastic dielectric waveguides are produced by injection mouldingand the dielectric waveguides fabricated have low propagation loss. Byusing injection moulding to manufacture the thermoplastic dielectricwaveguides, highly detailed structures can be stamped out with relativeease and at a relatively low cost. Therefore, the dielectric waveguidesof the present invention can be mass produced cost effectively. On theother hand, different thermoplastics and blended polymers can be used tomanufacture the dielectric waveguides. These different materials maypotentially provide valuable new functionalities to waveguide circuits.In sum, these factors together present a versatile and low-cost THzwaveguide circuit platform in accordance with the present invention.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

Any reference to prior art contained herein is not to be taken as anadmission that the information is common general knowledge, unlessotherwise indicated.

1. A dielectric waveguide comprising a dielectric probe at each end,wherein the dielectric probes are arranged to transfer energy.
 2. Adielectric waveguide in accordance with claim 1, wherein a core or acladding or both the core and the cladding of the dielectric waveguideare made of polymeric materials.
 3. A dielectric waveguide in accordancewith claim 2, wherein the polymeric materials include thermoplastics ora combination of thermoplastic materials.
 4. A dielectric waveguide inaccordance with claim 3, wherein the polymeric materials include one ofpolyethylene or polypropylene or combinations thereof.
 5. A dielectricwaveguide in accordance with claim 2, wherein the dielectric waveguideis fabricated by injection moulding.
 6. A dielectric waveguide inaccordance with claim 5, wherein the dielectric waveguide is fabricatedin a single mould.
 7. A dielectric waveguide in accordance with claim 5,wherein the dielectric waveguide is fabricated in multiple moulds.
 8. Adielectric waveguide in accordance with claim 1, wherein the dielectricwaveguide is a planar waveguide.
 9. A dielectric waveguide in accordancewith claim 1, wherein the dielectric probes are tapered.
 10. Adielectric waveguide in accordance with claim 9, wherein the dielectricwaveguide is operates at sub millimeter (Sub-mm) or terahertz (THz)frequencies.
 11. A dielectric waveguide in accordance with claim 9,wherein the dielectric probes have a linear tapered form.
 12. Adielectric waveguide in accordance with claim 11, wherein the dielectricwaveguide is operates at sub millimeter (Sub-mm) or terahertz (THz)frequencies.
 13. A dielectric waveguide in accordance with claim 1,wherein the dielectric probes are power adaptor probes.
 14. A dielectricwaveguide in accordance with claim 13, wherein the dielectric waveguideis operates at sub millimeter (Sub-mm) or terahertz (THz) frequencies.15. A dielectric waveguide in accordance with claim 1, wherein thedielectric waveguide is operates at sub millimeter (Sub-mm) or terahertz(THz) frequencies.
 16. A dielectric waveguide in accordance with claim15, wherein the terahertz (THz) frequencies comprise frequencies largerthan 60 GHz.
 17. A dielectric waveguide in accordance with claim 16,wherein the dielectric waveguide has a propagation loss less than 0.5dB/cm.